It has now been discovered that polymer liquid crystals such as polysaccharide liquid crystals can be made to encapsulate and deliver nutrients such as vitamins, minerals, or flavors to foods; sunscreens, emollients, antiseptics, perfumes, hair or skin care ingredients to health care products e.g. soaps, toothpaste, shampoos, creams, and lotions.
The liquid crystalline state exists between the boundaries of the solid phase and the isotropic liquid phase (i.e. an intermediate between the three dimensionally ordered crystalline state and the disordered dissolved state). In this state some of the molecular order characteristics of the solid phase are retained in the liquid state because of the molecular structure and short range intermolecular interaction. The ability of some compounds to form a liquid crystalline mesophase had been observed nearly a century ago. Since that time many compounds exhibiting liquid crystalline properties have been synthesized. D. Sek: Structural variations of liquid crystalline polymer macromolecules; Acta Polymerica, 39 (1988) No. 11, p. 599.
Low molecular weight organic surface active compounds (emulsifiers) are distinguished from polymers. The latter comprise large molecules made up of repeating units while the former are low molecular weight compounds. Physically and chemically, these two subclasses of materials are different from each other.
Low molecular weight liquid crystals, i.e. liquid crystals formed from a low molecular weight emulsifier or organic amphiphile (a compound having both a polar and a non-polar group, as a soap, lecithins or long chain fatty acid monoglyceride) are known to encapsulate and act as a delivery vehicle for drugs, flavors, nutrients and other compounds. Because of their weight, they are added at higher concentrations to achieve the same functionality as polymer liquid crystals which are made of a polymer and a solvent. The polymers can be a long chain of repeating units of amphiphiles or polymerized low molecular weight materials. They also form different types of liquid crystals.
Amphiphile molecules contain both hydrophilic and lipophilic grouping. They are substances exhibiting a marked tendency to adsorb at a surface or interface. Thus, surfactants are amphiphilic molecules divided into nonionic (no charge), ionic anionic (negative charge) and cationic (positive charge) and amphoteric (both charges) based on whether or not they ionize in aqueous media. Surfactants are also commonly called emulsifying agents. They are usually classified as lipids, which are fat-like substances. Surfactants are monomers (one structural unit), and are derived from natural oils and fats and crude oils.
The polymers of this invention are polysaccharides. They belong under the general group of carbohydrates, in contrast to surfactants or lipids. Carbohydrates are polyhydroxy compounds of the general formula (CH.sub.2 O)n, of which glucose (glu) is an example. Polysaccharides are carbohydrates derived from monosaccharides by the removal of n-1 molecules of water from n-molecules of monosaccharides. In polysaccharides, sugar monomers repeat, i.e. Glu-(Glu).sub.n -Glu-. Gums, fibers and hydrocolloids also may be classified as polysaccharides. They can be natural, biosynthetic, or modified. Their origin can be plant or microbial polysaccharides. Because polysaccharides are all compounds of higher molecular weight, they have the properties generally associated with colloids.
In the literature, liquid crystals are also referred to as anisotropic fluids, a fourth state of matter, polymer association structure or mesophases. Those terms are used interchangeably. The term "polymer liquid crystals" as used herein means "polymeric lyotropic liquid crystals" unless otherwise specified. The term "lyotropic" means a liquid crystalline system containing a solvent. This type of liquid crystal is distinguished in the art from thermotropic, heat or magnetically induced, liquid crystals. The same compound can form lyotropic and thermotropic liquid crystals.
A general description of the phase behavior of a soluble polymer in a solvent is as follows: (I) The polymer dissolves in the solvent to form an isotropic polymeric solution. (II) When the concentration of the polymer increases, a biphasic region which is a mixture of isotropic polymeric solution+liquid crystals is formed. (III) When the level of the polymer increases further and the required mixing is applied, a homogeneous single-phase liquid crystal range is induced. (IV) When even more polymer is present, a mixture of liquid crystals and crystalline polymer forms. (V) When extremely large amounts of polymer are present a crystalline and/or partially crystalline phase are present.
It is important to understand that liquid crystals are substances that possess mechanical properties resembling those of fluids yet are capable of transmitting polarized light (birefringence) under static conditions. In some cases they may show Bragg reflections characteristic of a well-defined molecular spacing. They have high degrees of orientational order and chain extensions.
Polymeric lyotroptc liquid crystals are subdivided into three subclasses: I. nematic, II. cholesteric, and III. smectic, which are optically anisotropic. See J. H. Wendorff, in "Scattering in Liquid Crystalline Polymer Systems" in "Liquid Crystalline Order in Polymers," A. Blumstein (ed.), Academic Press, Chapter 1 (1978).
I. In the nematic liquid crystalline phase the centers of gravity of the polymeric particles are arranged at random, consequently no positional long range order exists. Within volume elements of a macroscopic sample, the axes of all particles are oriented in a specific direction. Near the smectic-nematic transition temperature, there may be an additional ordering (positional order).
II. The cholesteric liquid crystalline phase is often thought of as a modification of a nematic phase, since its molecular structure is assumed to be similar to the latter. No positional order but only an orientational order exists in the cholesteric phase. In contrast, however, to the nematic phase, the cholesteric phase is characterized by the fact that the direction of the long axes of the molecules change continuously within the sample. This leads to a twist about an axis perpendicular to the long axes of the molecule.
III. In the smectic phases the centers of gravity of the elongated molecules are arranged in equidistant planes and smectic layers are formed. The planes are allowed to move perpendicularly to the layer normal and within the layers different arrangements of the molecules are possible. The long axes of the molecules can be parallel, normal or tilted with respect to the layer. A two-dimensional short range order or a two-dimensional long range order can exist within the smectic layers. The smectic modifications are labeled according to the arrangement of the particles within the layers.
Investigations of miscibility between different liquid crystalline modifications allow the distinction between various smectic phases and between smectic, cholesteric and nematic phases.
The light microscopy of liquid crystals is described in The Microscopy of Liquid Crystals, Norman Hartshorne, Microscopy Publications, Ltd., Chicago, Ill., U.S.A., 1974. Birefringence occurs in general for mesomorphic states. Methods for microscopic observation and evaluation are discussed in Chapter 1, pp.1-20, and cholesteric mesophase (liquid crystal) systems are discussed in Chapter 6, pp. 79-90. A preferred method for determining occurrence of liquid crystals is by observing birefringence of thin liquid crystal films between glass slides or from thin slices of a material under a polarizing microscope.
Focusing on the polymeric lyotropic liquid crystals of the present invention, in general, they are prepared by mixing the polymer with a sufficient amount of a solvent within the critical concentration and temperature ranges. The polymeric liquid crystalline phase flows under shear and is characterized by a viscosity that is significantly different from the viscosity of its isotropic solution phase. In other words, for some polymers, as the concentration increases, the viscosities of the polymer/solvent mixture increases until it reaches a viscosity peak. Then the viscosity decreases dramatically. The presence of such viscosity peaks signifies the onset of, or the presence of, a polymeric lyotropic liquid crystalline order. Hence, liquid crystals are distinguishable from polymeric systems which are isotropic solutions, pure solids, simple mixtures of solids and liquids and rigid isotropic polymeric gels. Rigid gels do not flow under shear like liquid crystals. Also, when viewed with a polarized light microscope, liquid crystals show identifiable birefringence, as, for example, planar lamellar birefringence, whereas when isotropic solutions and rigid gels are viewed under polarized light, both show dark fields.
Liquid crystal xanthan gum (a polymer) is reported to stabilize an oil-in-water emulsion (Biological Abstract 79:12413, Food Research Institute, Norwich, U.K. and M. Hennock et al., J. Food Sci., 49,1271, (1984).
Adding isotropic solutions of the polysaccharide in polar solvent to a fat, oil or other hydrophobic medium would lead to unacceptable results. If the polysaccharide were soluble in the solvent, the solvent nevertheless would not mix well with the medium. The solution would be expected to separate from the fat during storage or use. Flowable polysaccharide liquid crystals, on the other hand, allow substantial amounts of polysaccharide to be incorporated into a hydrophopic medium. Such mixtures can substitute for fats or oils in a variety of edible, fat-containing products without suffering the drawbacks of nonliquid crystal technology, i.e. gritty taste, and in both edible and non-edible products without separation or syneresis.
It is particularly desirable that the delivery vehicle composition be made from ingredients that are presently used and approved for use in edible product applications and for applying to the skin.
It is also an object of this invention to provide an encapsulating system to the food without affecting the mouth feel and taste of the product.
It is also an object of this invention to provide an encapsulating system which can be made with a minimum of processing and which is easily mixed with the food.
It has now been found that the above objects, as well as other benefits, can be attained by substituting liquid crystals formed from polysaccharides and solvents for conventional encapsulating agents, e.g. dextrins, gels, high melting fats, etc. present in certain foods and household items.